We got a trade in 420 manual shift, nearly a year ago, in good order apart from the usual smashed back plastic. However it idled slightly high, enough to make it move if in gear, and make changing back out of gear difficult. Did the usual EFI checks, no fault codes, so changed fuel filter, cleaned injector and ICAV. Changed ICAV when that didn't work. The symptoms were, it would start up, taking slightly longer than most 420s and idle OK until you opened the throttle. It would then idle a lot higher and "hunt" slightly. After checking the butterfly lever was hitting it's stop, I assumed it must be the throttle position sensor and reluctantly ordered a new one (expensive). Fitted it, did the TPS rest procedure and the bike was no different. Finally we got an identical bike in part exchange and I swapped everything from one to t'other. Temp sensors, throttle body, nothing fixed it. Finally tried putting the ECU from the faulty bike onto the "good one" instantly the fault transferred to the other bike. So a new ECU cured the problem.